1. Field of the Invention
This invention relates to the field of assembly of electronic components and more particularly relates to the connection or fastening of contact pins to a substrate.
2. Description of the Prior Art
Integrated circuit chips are mounted on ceramic bases or substrates, which provide surfaces on which circuit lines are formed that connect the integrated circuit with other portions of the electronic system. The substrates are usually formed by dry molding ceramic material, such as alumina, at high pressure and temperature. Interconnections are made between the circuits of one substrate and the circuits of other substrates by contact pins that are engaged by suitable electronic connectors. The contact pins are generally connected mechanically to the substrates by the application of slowly applied mechanical compression forces, which deform the pin and produce a pin head and collar or bulge between which the substrate is located.
It is difficult to successfully fabricate a satisfactory substrate and contact pin assembly. One difficulty arises because the contact pins must be accurately positioned in the holes of the substrate provided to receive the pins. Furthermore, the ceramic substrate is brittle and easily cracks or chips when subjected to excessive forces, particularly those that produce tension stress, for which the ceramic materials have a well recognized low strength. The contact pins must be rigidly attached to this substrate, free from any movement relative to the substrate and preferably seal the holes in the substrate against the entrance of contaminating materials used at later stages of the fabrication process.
Various techniques and devices have been proposed to attach the pins to the ceramic substrate. As a consequence of the molding process by which the substrates are formed, the substrates have non-planar surfaces and surface irregularities which are more pronounced in substrates of larger size. The presence of these irregular surfaces causes a large percentage of the substrates to crack and fail during the pin fastening operation. For this reason, it has been the conventional practice to mechanically form the pin located in the substrate holes by the application of slowly applied forces that gradually deform the pin material and avoid the abrupt application of forces to the pins during the pinning operation. In the prior art, machines for connecting the pins to the substrate generally employ some elastic component that structurally isolates the substrate from the hard, inflexible surfaces of the dies that apply the compressive force to the pins. The pins are then mechanically deformed by the application of force on the end of the pin which extends above the substrate. However, bending movements are produced in the substrate when the forming force is applied to the pins because the elastic member on which the substrate is supported is pressed against the substrate. Consequently when the forces are applied to the pins, bending moments are produced which induce tensile stresses through the thickness of the substrate and failure of the substrate often results.